1. Technical Field of the Disclosure
This embodiment relates in general to an efficient fan controller (EFC) for extending the fan run time of a HVAC systems after the heating or cooling unit has shut off. More specifically, the present embodiment is a new circuitry for changing the unknown state of the thermostat fan controller circuitry into a known state after the thermostat is turned off.
2. Description of the Related Art
Conventional HVAC (Heating Ventilating and Air Conditioning) systems include temperature changing components for changing the temperature and condition of air. Indoor air handlers drive air from the temperature changing component through supply ducts to zones within a building. A typical HVAC consists of heating unit, air conditioning unit and the fan or blower at the air handler unit. A thermostat is used to control the conditions of the air in a conditioned space by sending control signals to the HVAC furnace controller or HVAC air conditioning controller or HVAC fan controller to activate or deactivate one or more components.
Conventional HVAC fan controller typically operates the ventilation fan for 0 second to 90 seconds after the furnace or air conditional compressor has been turned off. Studies has shown that even after this 90 seconds duration, the furnace surface and the air conditioner cooling coil still has some energy left. This wasted energy is not delivered to the conditioned space when the fan stops blowing. Therefore there is a need in a HVAC system with a secondary fan controller device that can be used to recover additional heating and cooling capacity and operate HVAC equipment at higher efficiency.
The EFC will adjust the fan operation automatically for heating based on gas valve activation time or furnace operating time or Heat Pump activation time. For air conditioning, the same EFC will adjust fan operation automatically for cooling based on air-conditioning compressor run time. The amount of time the fan continues to operate after the furnace is off or after the air conditional compressor is off, varies with the amount of time the furnace or compressor are on using a microprocessor and firmware. The furnace additional fan run time indicates how much left over heat is stored in the heat exchanger. The air conditioner compressor additional run time indicates how much cold water is condensed on the evaporator coil. Hence, the EFC recovers and delivers more heating and cooling energy to the conditioned space than is possible with original HVAC fan controllers. The EFC improves the efficiency of HVAC equipment by delivering additional heating or cooling capacity for a small amount of additional electric energy (kWh).
Air conditioners cool conditioned spaces by removing sensible and latent heat from the return air which reduces the supply air temperature and humidity. Latent heat is removed as water vapor is condensed out of the air due to the temperature of the evaporator coil being less than the return air dew point temperature. Latent heat is the quantity of heat absorbed or released by air undergoing a change of state, such as water vapor condensing out of the air as water onto a cold evaporator coil or cold water evaporating to water vapor which will cool the air. Most evaporators are cold and wet (below 40 to 50° F.) after the compressor turns off. Cooling energy left on the evaporator coil after the compressor turns off is generally wasted. The evaporator absorbs heat from the attic and cold water on the coil flows down the condensate drain. The EFC recovers the remaining cooling energy from evaporator coil by operating the fan after the compressor turns off to cool the conditioned space.
Most furnace heat exchangers are still hot (above 135 to 210° F.) after the furnace fan turns off. The EFC recovers the remaining heat energy from the hot furnace heat exchanger after the furnace turns off and delivers this heat to the conditioned space. The EFC works by hijacking the fan control signals emitted by the thermostat and replace it with the new fan control signal emitted by the EFC itself. In this way, the HVAC fan controller only receives the fan control signals from the EFC itself and not from the thermostat directly. When the thermostat sends out the fan activate or deactivate command signal, it goes only to the EFC. The EFC reads this command and commands from the other environmental conditions plus from the HVAC components and computes the additional fan run time. Then, the EFC sends the adjusted command signal to the HVAC fan controller requesting it to run for a programmed additional extended time. Therefore, the EFC depends on the fan command signal emitted by the thermostat as source of input. The command signal of a thermostat is either a high of 24 vac or 0 vac (ground). Correspondingly, the EFC accepts either 24 vac or 0 Vac as its inputs.
For the EFC to work universally, it has to interface with every manufacturers of thermostats used in HVAC system. There are many manufacturers of thermostats where the fan output command signal goes into a floating or unknown state when the thermostat is shut off by putting the thermostat switch to system off. In such a case, if an EFC is connected to the thermostat, the fan command signal being in to unknown state could be read in as ON state, and the EFC will turn the fan on and run continuously. Therefore, there is a need to have a circuit in the EFC circuitry to read any unknown or floating signals from the thermostat fan command signal as known 24 vac or 0 vac state. In this way, the fan will always be turned off when it is not at an ON state.
Further, there is a need for a HVAC system that would extend the fan run time and still shut the fan off when the thermostat fan output command signal is in a floating state. As such, it would be desirable to provide a simplified and lower cost EFC controller interface for an HVAC controller that could be easily operated by the user. Also such a needed system would solve the floating state of the thermostat fan output signal after the thermostat is turned off and keeps the HVAC fan in an OFF state.